A common type of lighting apparatus that has achieved great commercial success is the linear lighting arrangement, in which the lighting apparatus typically has an elongated profile lamp with light emission along the length of the lamp. These linear lamps are commonly used in office, commercial, industrial and domestic applications and incorporate standard size linear lamps (such as standard tubular T5, T8, and T12 lamps).
A linear lighting apparatus that is commonly used in office and commercial applications is a ceiling-recess or troffer that is mounted within a modular suspended (dropped) ceiling. Other, linear lighting apparatus include suspended linear arrangements that can be direct only (downward light emitting) or direct/indirect (lighting both the workspace in a downward direction and the ceiling in an upward direction for indirect lighting. Surface mount linear fixtures, often called wraparound lights or wrap lights, are used in both office, industrial and domestic spaces. These are typically mounted directly to the surface of the ceiling or wall. Task lighting and under-cabinet fixtures also common use linear tubular lamps as the light source.
While traditional fluorescent tube troffers, suspended linear, wraparound lights and under-cabinet lighting arrangements are very common and exist in almost every commercial office building, there are many disadvantages associated with such lighting configurations. The conventional linear configurations tend to be relatively complex, given the number of disparate components (e.g., troffer housing, lamp connectors, lamp driver, separate diffusers, doors/panels, tubes) that need to be separately manufactured and then integrated together in the lighting arrangement. In addition, since each lamp (tube) requires electrical connection to each end, cabling has to be provided over a significant portion of the volume of the arrangement requiring greater and more extensive safety-related and certification-related reinforcements to the lighting fixture/troffer, increasing the size and weight of the arrangement. Moreover, fluorescent tubes in the conventional troffers suffer from spotty reliability and relatively inefficient lighting uniformity and performance. These problems therefore negatively affect the complexity, performance, weight, and/or cost to anyone that seeks to manufacture or install a linear light.
In addition, many disadvantages are also associated with the use of conventional fluorescent-based tube technology, which are gas discharge lamps that use electricity to excite mercury vapors. For example, the mercury within the fluorescent lamp is poisonous, and breakage of the fluorescent lamp, particularly in ducts or air passages, may require expensive cleanup efforts to remove the mercury (as recommended by the Environmental Protection Agency in the USA). Moreover, fluorescent lamps can be quite costly to manufacture, due in part to the requirement of using a ballast to regulate the current in such lamps. In addition, fluorescent lamps have fairly high defects rates and relatively short operating lives.
Recently, white light emitting LEDs (“white LEDs”) have become more popular and more commonly used, replacing conventional fluorescent, compact fluorescent and incandescent light sources. White LEDs generally include one or more photo-luminescent materials (e.g., one or more phosphor materials), which absorb a portion of the radiation emitted by the LED and re-emit light of a different color (wavelength). The phosphor material may be provided as a layer on, or incorporated within a wavelength conversion component that is located remotely from the LED die. Typically, the LED generates blue light and the phosphor(s) absorbs a percentage of the blue light and re-emits yellow light or a combination of green and red light, green and yellow light, green and orange or yellow and red light. The portion of the blue light generated by the LED that is not absorbed by the phosphor material combined with the light emitted by the phosphor provides light which appears to the eye as being nearly white in color. Such white light LEDs are characterized by their long operating life expectancy (>50,000 hours) and high luminous efficacy (70 lumens per watt and higher).
For white LEDs, light is generated by two processes: electroluminescence and photoluminescence (rather than thermal radiation). Thus, the emitted radiation does not follow the form of a black-body spectrum. These sources are assigned what is known as a correlated color temperature (CCT). CCT is the color temperature of a black body radiator which to human color perception most closely matches the light from the lamp. Color temperature is a characteristic of visible light that has important applications in lighting. The color temperature of a light source is a measurement of the hue generated by that light source that corresponds to the temperature of an ideal black-body radiator that radiates light of comparable hue. Color temperature is conventionally stated in the unit of absolute temperature, the kelvin, having the unit symbol K. Color temperatures over 5,000 K are called cool colors (blueish white), while lower color temperatures (2,700-3,000 K) are called warm colors (yellowish white through red)
Traditional incandescent light bulbs are configured to generate light of varying brightness during dimming operation. A dimmer switch typically controls the power provided to the light bulb. The larger the power provided to the light bulb, the greater the temperature of the light bulb filament and the brighter the light generated. For an incandescent light bulb, light is generated by thermal radiation and so its color temperature is essentially the temperature of the filament. Typical incandescent light bulbs generate light of a warm yellowish white hue (e.g., 2,700-3,000K) at full power and at lower powers, can produce light of an even warmer orangeish white hue (e.g., 1500K) that is not available in non-incandescent light bulbs.
Whereas some incandescent light bulbs are capable of generating light that ranges from a warm yellowish white to a warmer orangeish white, white LED light emitting devices (e.g., LED-based linear lamps) do not exhibit these same characteristics. This is because the color temperature of an incandescent light bulb changes in response to the power provided to the bulb, whereas the correlated color temperature (CCT) of a white LED light emitting device changes in response to variations in photo-luminescent material or the material from which the LED is fabricated. Because the photo-luminescent materials and LED materials are fixed, when the power applied to the white LED light emitting device is lowered, the intensity of the emission product changes, but the correlated color temperature remains the same.
Thus, a problem with such devices involves the dimming/correlated color temperature (CCT) characteristics of such devices. Moreover, while some incandescent lights may be capable of generating light with a range of color temperatures between warm yellowish white and even warmer orangeish white, it may be desirable to have an even larger range of color temperatures. For example, a restaurant may want to tune a light bulb to generate bright bluish white light for large parties to create an exciting atmosphere and softer yellowish white light for intimate gatherings to create a warm and romantic atmosphere.
As is evident, there is a need for an improved approach to implement linear lighting arrangements that overcome the drawbacks of the conventional linear lamps.